Double-wall plastic produce container having ventilation holes therein, and mold for the manufacture thereof

ABSTRACT

In this ventilated double-wall plastic container, each hole structure has a central hole surrounded by a solid flange extending along the inside wall of the double-wall structure. The hole structure also has a spacer portion connecting the solid flange to the outside wall of the double-wall structure. The wall segments of the hole structure between the spacer portion and the flange and between the spacer portion and the outside wall of the container define angles that are either obtuse angles or right angles. In another aspect, the mold for manufacturing the double-wall container has spaced-apart inside and outside metal walls, a plurality of openings in the outside metal wall, and hole-forming inserts mounted in the openings and projecting toward the inside wall. A projecting surface on each of the hole-forming inserts defines with the inside wall a space of even thickness surrounding a pin at the centre of the insert.

FIELD OF THE INVENTION

This invention pertains to double-wall produce containers havingventilation holes therein, and more particularly it pertains todouble-wall plastic produce containers having porosity-free holestructures therein. This invention also pertains to molds havinghole-forming inserts therein for manufacturing ventilated double-wallplastic containers using a rotational molding process.

BACKGROUND OF THE INVENTION

Fruits and vegetables are commonly harvested in plastic containers thatare stacked on a harvesting machine and transported to a storagefacility. These containers are generally made with a double-wallstructure for increased sturdiness, to better resist stacking andhandling stresses. These double-wall plastic containers are generallymanufactured using rotational molding processes.

Fruits such as blueberries are harvested at the end of the summer whenambient temperatures are relatively high. Therefore, the containers thatare used to harvest blueberries must have ventilation holes therein toprevent deterioration of the fruits due to heat and airless confinement.The surface of these containers must be free of crevices and pin holesand must have an overall surface texture that is well adapted to bedisinfected with steam or detergent and water for example.

The surface of these containers must also be sealed to prevent moisture,dust, dirt or other impurities from migrating into the plastic material,or from penetrating inside the hollow space of the double-wall structureof the container.

It has always been a challenge in the rotational molding industry toform ventilation holes in a double-wall plastic container withoutcausing porosity to occur around these holes.

Examples of prior art double-wall plastic articles having holes thereinare shown in the following documents:

U.S. Pat. No. 3,506,154 issued to Tracy W. Barnes on Apr. 14, 1970;U.S. Pat. No. 6,155,580 issued to Ronny Symons on Dec. 5, 2000.

Both examples illustrate common hole structures in double-wall plasticarticles made by rotational molding processes. For comparison purposes,the common hole structure 20 as found in the prior art articles isillustrated in the accompanying drawings. In FIGS. 2 and 3, the hole 22in one wall 24 is larger than the hole 26 in the other wall 28 of adouble-wall article, and both holes are joined by a conical section 30.This type of hole structure makes it easy to remove a molded articlefrom a mold, and therefore, it has been widely used in the rotationalmolding industry.

It has also been found that it is very difficult to eliminate porosityfrom this type of hole structure, and especially from the regionidentified by the detail circle 32 in FIG. 3. For this reason, this typeof hole structure has been found unsuitable for application in adouble-wall plastic container that is used for carrying blueberries forexample. As such it is believed that a need still exists in theagricultural industry for double-wall plastic produce containers havingporosity-free ventilation holes therein.

SUMMARY OF THE INVENTION

In the present invention, however, there is provided a double-wallplastic container having porosity-free hole structures therein. There isalso provided a mold with hole-forming inserts therein for molding adouble-wall ventilated container in a rotational molding process.

In one aspect of the container according to the present invention, eachhole structure comprises a central hole surrounded by a flat solidplastic flange extending at right angle from the central hole, and alongthe inside wall of the double-wall structure. The hole structure alsohas a spacer portion connecting the solid flange to the outside wall ofthe double-wall structure of the container. The wall segments of thehole structure between the spacer portion and the flange and between thespacer portion and the outside wall of the container define angles thatare either obtuse angles or right angles. The thickness of the flange isat least 0.75 times the thickness of one of the walls in the double-wallstructure. This hole structure is advantageous as it is moldable withoutgenerating porosity around the central hole thereof.

In another aspect of the present invention, the mold for manufacturingthe above-mentioned container has spaced-apart inside and outside metalwalls, a plurality of openings in the outside metal wall, andhole-forming inserts mounted in the openings and projecting toward theinside metal wall.

The hole-forming inserts are made of metal and each has a metal pinextending therefrom and against the inside wall. A projecting surface oneach of the hole-forming inserts extends from the outside wall towardthe inside wall and defines with the inside wall a space of eventhickness surrounding the pin. This projecting surface on each of theinserts makes an obtuse angle with the space of even thickness and aright angle with the pin.

When a container is formed therein, the hole-forming insert, the pin andthe space of even thickness define a region inside the mold that issurrounded by hot metal and wherein plastic pellets or plastic powdercan easily penetrate and be evenly melted, for preventing the occurrenceof porosity in the molten plastic around the hole.

In yet another aspect of the present invention, each hole-forming inserthas a spring mounted therein and this spring acts against the metal pinfor pushing the pin against the inside wall of the mold. The force ofthe spring ensures a good contact between the pin and the inside wall ofthe mold, and a better heat transfer coefficient between the metal pinand the inside wall of the mold.

This brief summary has been provided so that the nature of the inventionmay be understood quickly. A more complete understanding of theinvention can be obtained by reference to the following detaileddescription of the preferred embodiment thereof in connection with theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of a double-wall container having ventilation holestherein is illustrated in the accompanying drawings, with threepreferred hole structures therefor being illustrated in greater details.In these drawings the same numerals are used to identify the sameelements.

FIG. 1 is an isometric view of a stackable, double-wall, plastic producecontainer according to a preferred embodiment of the present invention;

FIG. 2 is a perspective view of a hole structure of the prior art;

FIG. 3 is a cross-section view of the hole structure of the prior art asseen along line 3-3 in FIG. 2;

FIG. 4 is a perspective view of a first preferred hole structure;

FIG. 5 is a cross-section view of the hole structure illustrated in FIG.4, as seen along line 5-5 in FIG. 4;

FIG. 6 is a cross-section view of a second preferred hole structure, anda cross-section view of a hole-forming insert that is used for formingthis second preferred hole structure;

FIG. 7 is a cross-section view of a third preferred hole structure, anda cross-section view of a hole-forming insert that is used for formingthis third preferred hole structure;

FIG. 8 is a perspective view of the hole-forming insert for forming thesecond preferred hole structure;

FIG. 9 is a perspective view of the hole-forming insert for forming thethird preferred hole structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

While this invention is susceptible of embodiment in many differentforms, there are shown in the drawings and will be described in detailsherein one specific embodiment of a double-wall ventilated container,with three different preferred ventilation hole structures, with theunderstanding that the present disclosure is to be considered as anexample of the principles of the invention and is not intended to limitthe invention to the embodiment and preferred hole structuresillustrated and described.

For reference purposes, FIG. 1 illustrates a stackable, double-wallplastic produce container 34 with ventilation holes 36 according to oneof the preferred hole structures described and illustrated herein.

Referring now to FIGS. 4 and 5, the first preferred hole structure 40 isillustrated therein. The first preferred hole structure 40 isdistinguishable from the hole structure 20 of the prior art, as shown inFIGS. 2 and 3, for having a flat disc-like solid flange 42 surroundingthe hole 44, and extending at a right angle from the hole 44.

The first preferred hole structure 40 has a large hole 46 in the outsidewall 48 of the double-wall structure of the container, and a conicalsection 50 extending from the outside wall 48 to the flange 42. The hole44 has a cylindrical shape and extends through the centre of the flange42. In this preferred hole structure, the flange 42 is integrated withthe inside wall 52 of the container and is flush with the inside wall.

Preferably, the diameter ‘A’ of the disc-like flange 42 is about threetimes the diameter ‘B’ of the hole 44. The flange thickness ‘C’ ispreferably equal to or larger than about 0.75 times the wall thickness‘T’ of one of the walls 48, 52 in the double-wall structure of thecontainer 34.

Preferably, the flange 42 is flush with the inside wall 52 of thecontainer, as mentioned above, but can also be positioned at anintermediate distance between both walls, with two conical sections 50extending respectively to each wall 48, 52.

Referring now to FIGS. 6-9, the hole-forming inserts 56, 58 for formingtwo of the preferred hole structures will be explained. In the firsthole-forming insert 56, as illustrated in FIGS. 6 and 8, the insertcomprises a cup-like member 60 which is adapted to be mounted in anopening 62 through the outside wall 64 of a mold. The cup-like member 60is preferably welded to the outside wall 64 of the mold, as illustrated,but can also be mounted to the mold with fasteners.

The cup-like member 60 has a threaded hole 66 through its centre. Athreaded plug 68 is mounted into the threaded hole 66 and is adjustablerelative to the cup-like member 60. A locknut 70 on the threaded plug 68is used to retain the plug 68 at a desired position relative to thecup-like member 60.

The threaded plug 68 has a hollow core 72. A spring 74 is mounted in thehollow core, and a metal pin 76 is slidably mounted in the hollow corebelow the spring. In a blueberry container, the metal pin 76 could havea diameter of ¼ inch for example. A head 78 on the pin 76 holds thespring captive against the bottom end of the hollow core 72. In use, thespring 74 pushes the pin 76 against the inside wall 80 of the mold, asillustrated in FIGS. 6 and 7.

It should be understood that the side walls 64, 80 of the mold are madeof metal. The hole-forming inserts 56, 58 are also made of metal and aremounted to absorb heat from both side walls 64, 80.

The rate of the spring 74 is selected, and the initial compression ofthe spring may be adjusted by turning the threaded plug 68 and thelocknut 70, to ensure that there is a good contact between the end ofthe metal pin 76 and the inside wall 80 of the mold when the mold inclosed, such that there is good heat transfer coefficient between theinside wall 80 of the mold and the pin 76.

The hole-forming insert 56 is used for forming a ventilation hole thatis enclosed by a spherical depression 82, as may be understood from theillustration in FIGS. 6 and 8. The second hole-forming insert 58 has abar-like, trapezoidal body 90, as illustrated in FIGS. 7 and 9. Thissecond hole-forming insert 58 can be used to form ventilation holesinside a reinforcing rib on a container, such as the rib 92 illustratedin FIG. 1.

It will also be appreciated that the hole-forming insert 56 can also bemodified so that the cup-like member has a conical shape. The holeformed with it would have a same cross-section as in the illustration inFIG. 7, and an appearance as illustrated in FIGS. 4 and 5. It will alsobe appreciated that the spherical cup-like member 60 can also bereplaced by a cylindrical shaped member (not shown) to obtainsubstantially the same advantageous results as those mentioned herein.

For reference purposes the conical section 50 and the spherical section82 are also referred to herein as the spacer means because theseelements are used for retaining both walls of the double-wallconstruction at a proper distance from each other around a hole 44.

Referring again to FIG. 7, it will be appreciated that the angles of theplastic walls around the third preferred hole structure, at ‘D’, ‘E’,‘F’ and ‘G’ are obtuse angles or right angles. The same obtuse and rightangles can be found in the first and second preferred hole structures asillustrated in FIGS. 5 and 6. The relatively large angles along thepreferred hole structures are believe to be a contributing factor forpreventing the formation of porosity in the plastic material during themolding process. A good heat transfer between the inside wall 80 of themold and the pin 76 is also another important contributing factor forpreventing the formation of porosity in the preferred hole structures.

While three hole structures for preventing the formation of porosity inthe plastic material of a double-wall container, have been illustratedin the accompanying drawings and described herein above, it will beappreciated by those skilled in the art that various modifications,alternate constructions and equivalents may be employed withoutdeparting from the spirit and scope of the invention. Therefore, theabove description and the illustrations should not be construed aslimiting the scope of the invention, which is defined by the appendedclaims.

1. A double-wall plastic container having a double-wall structurecomprising a first and second spaced-apart walls, and ventilation holestherein; each of said ventilation holes having a hole structurecomprising a central hole surrounded by a flange made of solid plastic,and spacer means connecting said flange to said first wall, whereinsegments of said spacer means connected to said flange and to said firstwall define angles of 90° or more.
 2. The double-wall plastic containeras claimed in claim 1, wherein said flange extends perpendicularly fromsaid central hole.
 3. The double-wall plastic container as claimed inclaim 2, wherein said central hole has a diameter and said flat flangehas a width of about three times said diameter.
 4. The double-wallplastic container as claimed in claim 3, wherein said first and secondwalls have a similar wall thickness and said flange has a flangethickness of at least 0.75 times said wall thickness.
 5. The double-wallplastic container as claimed in claim 4, wherein said flange extendsalong and flush with said second wall.
 6. The double-wall plasticcontainer as claimed in claim 1, wherein said spacer means has a conicalshape.
 7. The double-wall plastic container as claimed in claim 1,wherein said spacer means has a spherical shape.
 8. The double-wallplastic container as claimed in claim 1, further having ribs therein,and one of said ventilation holes is located in one of said ribs, andsaid spacer means define sides of said rib.
 9. A double-wall plasticcontainer having a double-wall structure comprising a first and secondspaced-apart walls, and ventilation holes therein; each of saidventilation holes having a hole structure comprising a central holesurrounded by a flange made of solid plastic and extending along andflush with said first wall at a right angle from an axis of said centralhole, said flange having a width of about three times a diameter of saidcentral hole; and spacer means connecting said flange to said secondwall, wherein segments of said spacer means connected to said flange andto said second wall define obtuse angles.
 10. The double-wall plasticcontainer as claimed in claim 9, wherein said first and second wallshave a similar wall thickness and said flange has a flange thickness ofat least 0.75 times said wall thickness.
 11. The double-wall plasticcontainer as claimed in claim 9, wherein said flange has a disc-likeshape.
 12. A mold for molding a ventilated, double-wall container by arotational molding process; said mold comprising spaced-apart inside andoutside walls; an opening is said outside wall; a hole-forming insertmounted in said opening; said hole-forming insert having a pin extendingtherefrom and against said inside wall, and a projecting surfaceextending toward said inside wall and defining with said inside wall aspace of even thickness surrounding said pin.
 13. The mold as claimed inclaim 12, wherein said space of even thickness extends perpendicularlyfrom said pin.
 14. The mold as claimed in claim 12, wherein saidhole-forming insert comprises a compression spring mounted thereinagainst an end of said pin for pushing said pin against said insidewall.
 15. The mold as claimed in claim 13, wherein said projectingsurface has a spherical shape, a conical shape or a cylindrical shape.16. The mold as claimed in claim 14, wherein said hole-forming insertcomprises a threaded hollow plug adjustably mounted therein and said pinand said spring are mounted inside said threaded hollow plug.
 17. Themold as claimed in claim 12, wherein said projecting surface makesobtuse angles with said outside wall and with said space of eventhickness.
 18. The mold as claimed in claim 12, wherein saidhole-forming insert comprises a bar-like trapezoidal body defining saidprojecting surface.
 19. The mold as claimed in claim 13, wherein saidspace of even thickness has a width of about three times a diameter ofsaid pin.
 20. The mold as claimed in claim 13, wherein said space ofeven thickness has a disc-like shape.